Polyester fiberfill filling material (sometimes referred to herein as polyester fiberfill) has become well accepted as a reasonably inexpensive filling and/or insulating material especially for pillows, and also for cushions and other furnishing materials, including other bedding materials, such as sleeping bags, mattress pads, quilts and comforters and including duvets, and in apparel, such as parkas and other insulated articles of apparel, because of its bulk filling power, aesthetic qualities and various advantages over other filling materials, so is now manufactured and used in large quantities commercially. "Crimp" is a very important characteristic. "Crimp" provides the bulk that is an essential requirement for fiberfill. Slickeners, referred to in the art and hereinafter, are preferably applied to improve aesthetics. As with any product, it is preferred that the desirable properties not deteriorate during prolonged use; this is referred to generally as durability. Hollow polyester fibers have generally been preferred over solid filaments, and improvements in our ability to make hollow polyester fiberfill with a round periphery has been an important reason for the commercial acceptance of polyester fiberfill as a preferred filling material. Examples of prior cross-sections are those with a single longitudinal void, such as disclosed by Tolliver, U.S. Pat. No. 3,772,137, and by Glanzstoff, GB 1,168,759, and multi-void fibers, including those with 4-holes, such as disclosed in EPA 2 67,684 (Jones and Kohli), and those with 7-holes, disclosed by Broaddus, U.S. Pat. No. 5,104,725, all of which have been used commercially as hollow polyester fiberfill filling material. Most commercial filling material has been used in the form of cut fibers (often referred to as staple) but some filling material, including polyester fiberfill filling material, has been used in the form of deregistered tows of continuous filaments, as disclosed, for example by Watson, U.S. Pat. Nos. 3,952,134, and 3,328,850. We use herein both terms "fiber" and "filament" inclusively without intending use of one term to exclude the other.
Generally, for economic reasons, polyester fiberfill fiber filling material, especially in the form of staple, has been made bulky by mechanical crimping, usually in a stuffer box crimper, which provides primarily a zigzag 2-dimensional type of crimp, as discussed, for example, by Halm et al in U.S. Pat. No. 5,112,684. A different and 3-dimensional type of crimp, however, can be provided in synthetic filaments by various means, such as appropriate asymmetric quenching or using bicomponent filaments, as reported, for example, by Marcus in U.S. Pat. No. 4,618,531, which was directed to providing refluffable fiberballs (sometimes referred to in the trade as "clusters") of randomly-arranged, entangled, spirally-crimped polyester fiberfill, and in U.S. Pat. No. 4,794,038, which was directed to providing fiberballs containing binder fiber (in addition to the polyester fiberfill) so the fiberballs containing binder fiber could be molded, for example, into useful bonded articles by activating the binder fibers. Such fiberballs of both types have been of great commercial interest, as has been the problem of providing improved polyester fiberfill having "spiral crimp". The term spiral crimp is frequently used in the art, but the processes used to provide synthetic filaments with a helical configuration (perhaps a more accurate term than spiral crimp) does not involve a "crimping" process, in a mechanical sense, but the synthetic filaments take up their helical configuration spontaneously during their formation and/or processing, as a result of differences between portions of the cross-sections of the filaments. For instance, asymmetric quenching can provide "spiral crimp" in monocomponent filaments, and bicomponent filaments of eccentric cross-section, preferably side-by-side but also with one component off-centered, can take up a helical configuration spontaneously.
It has long been known that such helical bicomponent fibers have advantages over mechanically-crimped filling fibers, as disclosed, for example, by Clarke et al in U.S. Pat. No. 3,595,738. Clarke referred to such filaments as "possessing a three-dimensional crimp of the reversing helical type", and it is correct that the helixes are of the reversing helical type. For convenience herein, we shall mostly simply refer to such polyester fibers as being of helical configuration. However, Clarke emphasized that these advantages were "only apparent provided the scale of the helical crimp is within certain limits", and that "if the filaments have less than about 8 crimps per inch and a crimp index less than about 40%, the filling or stuffing material made therefrom has low resistance to compression". Clarke disclosed (in Table at top of cols 5 and 6) that the performance of webs of polyester fiber of "Sample No. 1 and Sample No. 2" having 7 and 8 "Average number of crimps" (per inch, i.e., 27.5 and 31.5 CPdm, crimps per dm), and with 39 and 52 "Average CI percent", was "Fibre carding poor; low web cohesion. Bulk: low resistance to compression", and that other samples, having at least 10 "Average number of crimps" (almost 40 CPdm), were "much superior" to those samples Nos 1 and 2.
Relatively few helical bicomponent fibers with longitudinal voids have been disclosed or been available hitherto. Clarke did not disclose any such fibers with voids. An improved type of bicomponent polyester multi-void fiberfill fiber of helical configuration (spiral crimp) has been disclosed by Hernandez et al. in U.S. Pat. Nos. 5,458,971 and 5,683,816. Hernandez also disclosed prior single void fibers sold commercially as H18Y by Unitika (who apparently also sell other hollow filaments referred to by other designations, such as H18X) and as 7-HCS by Sam Yang, and properties measured on such fibers, which are discussed hereinafter as comparisons.